/*
 * Copyright 2016 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.util.concurrent;

import io.netty.util.internal.ObjectUtil;

import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;

/**
 * Expose helper methods which create different {@link RejectedExecutionHandler}s.
 */
public final class RejectedExecutionHandlers {

  private static final RejectedExecutionHandler REJECT = new RejectedExecutionHandler() {
    @Override
    public void rejected(Runnable task, SingleThreadEventExecutor executor) {
      throw new RejectedExecutionException();
    }
  };

  private RejectedExecutionHandlers() {
  }

  /**
   * Returns a {@link RejectedExecutionHandler} that will always just throw a {@link
   * RejectedExecutionException}.
   */
  public static RejectedExecutionHandler reject() {
    return REJECT;
  }

  /**
   * Tries to backoff when the task can not be added due restrictions for an configured amount of
   * time. This is only done if the task was added from outside of the event loop which means {@link
   * EventExecutor#inEventLoop()} returns {@code false}.
   */
  public static RejectedExecutionHandler backoff(final int retries, long backoffAmount,
      TimeUnit unit) {
    ObjectUtil.checkPositive(retries, "retries");
    final long backOffNanos = unit.toNanos(backoffAmount);
    return new RejectedExecutionHandler() {
      @Override
      public void rejected(Runnable task, SingleThreadEventExecutor executor) {
        if (!executor.inEventLoop()) {
          for (int i = 0; i < retries; i++) {
            // Try to wake up the executor so it will empty its task queue.
            executor.wakeup(false);

            LockSupport.parkNanos(backOffNanos);
            if (executor.offerTask(task)) {
              return;
            }
          }
        }
        // Either we tried to add the task from within the EventLoop or we was not able to add it even with
        // backoff.
        throw new RejectedExecutionException();
      }
    };
  }
}
